Generally, networking devices and/or processes are divided into abstract layers to simplify understanding of the complexities of communication and to facilitate easier development and interfacing of the devices and/or processes with other devices and/or processes. The seven layer OSI (Open Systems Interconnect) model is a commonly used abstraction that includes: the level one physical layer, the level two data link layer, the level three network layer, the level four transport layer, the level five session layer, the level six presentation layer, and the level seven application layer. Generally, lower level protocol layers provide services for transporting higher level protocol layers.
For instance, in the past many service providers deployed various connection-oriented packet networks (such as X.25, frame relay, and/or ATM) that provided customers with the ability to forward traffic across permanent and/or switched virtual circuits (PVCs and/or SVCs). These connection-oriented, virtual-circuit packet networks of X.25, frame relay, and/or ATM (Asynchronous Transfer Mode) may have layer three functionality in the signaling messages used for establishing and releasing the virtual circuits. In addition, X.25 packets generally include level three packet layer procedures (PLP) for carrying user data. Frame relay and ATM at least partially evolved from X.25 but with a design goal of having less overhead and more efficiency than X.25. Thus, frame relay and ATM generally provide what is considered to be layer two service for carrying user data. However, these connection-oriented, virtual-circuit packet networks generally are known to provide a forwarding capability that generally passes information from other protocols (potentially at higher layers of the OSI model) inside packets, frames and/or cells of X.25, frame relay and/or ATM, respectively.
One skilled in the art should be aware of the similarities and differences among the connection-oriented packet-switching technologies of X.25, frame relay, and ATM as well as the common utilization of these virtual-circuit packet-switching technologies to provide connectivity for carrying layer three network protocols, such as but not limited to the Internet Protocol (IP). While frame relay and ATM generally are known as layer two networks, X.25 generally has a level three network layer. However, as a connection-oriented packet-switching technology, X.25 has similar characteristics to the layer two networks of frame relay and ATM with regard to carrying and/or encapsulating network layer packets of protocols such as IP over virtual circuits. In addition, CCITT/ITU (Comite Consultatif Internationale de Telegraphie et Telephonie/International Telecommunications Union) recommendation X.25 defines a DTE-DCE (Data Terminal Equipment—Data Communications Equipment) interface (or a user-network interface) to a packet switching network with the DTE-DCE interface based upon a virtual-circuit paradigm, and the term “X.25 network” is often used to mean a network that provides an external X.25 DTE-DCE interface.
With the increased deployment of certain layer three network protocols, especially including the Internet Protocol or IP (including both IP version 4 or IPv4 as well as IP version 6 or IPv6), customers have often used the forwarding capabilities of connection-oriented, virtual-circuit packet networks to provide interconnection of IP devices and networks located in distant locations. Usually, layer three IP networking technology may have developed on local area networks (LANs) within different buildings that later were interconnected using wide-area networks (WANs) often comprising connection-oriented, virtual-circuit packet-switching technologies.
In contrast to the connection-oriented, virtual-circuit packet-switching of X.25, frame relay, and/or ATM, IP networks primarily provide connectionless, datagram service. In IP networks, the packet switches usually are called routers. Connection-oriented, virtual-circuit packet-switching networks generally have a one-to-one or point-to-point relationship between the termination points of a virtual circuit. Unlike the connection-oriented networks, connectionless and/or datagram packet-switching networks generally do not have connections or circuits that establish a relationship between one termination point (or endpoint) and another termination point (or endpoint).
With the advent of newer technology such as but not limited to Multi-Protocol  Label Switching (MPLS), many service providers have been adding a layer three routed core to WAN technologies that previously had primarily just provided connection-oriented service using the virtual-circuit packet-switching technologies. Normally, service providers are deploying the new technology of routed cores in newer technology packet switching networks such as the layer two networks of frame relay and ATM; however, nothing prevents a service provider from adding a connectionless routed core to other connection-oriented networks such as, but not limited to, a network using the older connection-oriented, packet-switching technology of X.25. Prior to the more or less ubiquitous adoption of IP as the common layer three protocol for most networks, the plethora of layer three protocols made it relatively impractical for network service providers to implement layer three routing services within the service provider WANs. In addition to changes in the regulatory environment, the general industry standardization on IP as the common layer three protocol makes it more feasible for service providers to add IP routing functionality to networks that previously had primarily just provided connection-oriented, virtual-circuit packet-switching services such as but not limited to the services provided by the layer two networks of frame relay and ATM.
Unfortunately, adding higher layer services such as an IP routing core to a service provider's network creates some additional problems for customers. As described previously and as is well-known in the art, IP is a connectionless datagram protocol (or more accurately IP provides connectionless datagram service). As a result, IP generally does not establish a one-to-one relationship between two points in an IP network. Despite this general lack of a one-to-one relationship between IP devices, the relatively higher costs of connecting networks over the relatively longer distances of a wide area usually result in network configurations where all or almost all the traffic between two locations goes through one IP device at one location and through another IP device at the other location (at least when the complexities of redundant communication paths and/or devices are ignored). In the case of a virtual-circuit packet-switching network that just provides connection-oriented services, customers can use various mechanisms to easily detect the “health” of the network from the end points of the virtual circuit. Using these mechanisms, network administrators could quickly determine whether a remote site had lost connectivity or was suffering performance degradations.
Usually isolation of network failures involves evaluating the status of network devices and communication lines at the interface of ownership between the networks. Thus, customers like to be able to isolate a network problem to determine whether the problem exists in the customer's equipment and/or network or exists in the service provider's equipment and/or network. Usually the termination points of a WAN are common locations for the legal demarcation between customer equipment and service provider equipment. Thus, detecting the end points of the WAN as well as monitoring the health status and performance of these end points usually is important for quickly isolating network problems and assigning ownership of the problem such that the proper entity (service provider or customer) assigns the necessary human and technical resources to bypass and/or resolve the network problem.
The addition of an IP routing core, which introduced connectionless datagram service into the packet networks of service providers, prevents the previously easy detection of the end devices on a WAN and reduces the visibility of the customer's network administrator to network health and performance information. Because the addition of a routed core to service provider wide-area packet networks has undesirable drawbacks, a heretofore unaddressed need exists in the industry to automatically detect whether such a network has a routed core architecture and/or to compensate for the inadequacies of the architecture in providing network health and/or performance information.